This invention relates to filament-wound pressure vessels and, more particularly, to a filament-wound hydropneumatic accumulator tank containing a flexible diaphragm which separates the interior of the tank into a compressible gas-containing chamber and a liquid-containing chamber. In water system applications, there exists a need to provide a stored energy device that can provide instantaneous water pressure to some type of demand. To accomplish this, the pressure vessel has become an accepted method of providing this water pressure. The tank is generally connected in line with a supply source that has a pumping device. This pumping device is not capable of providing instantaneous pressure, nor is it recommended that the pumping device operate in a manner that is cycling in unison with the demand for the water. This can reduce the life of the pumping device. A pressure tank acts as a storage device that can supply water under pressure for low demand periods without requiring the pumping device to turn on. For higher demand periods, the tank will allow the pump to run for recommended minimum periods while not interrupting the demand requirements. In order for the tank to act in this manner, air under pressure contained in the tank is compressed as the water is pumped into the tank. As more water enters the tank, a pressure rise results, and the pump will shut off at a predetermined sensed pressure. The cycle will not repeat until a demand relieves the tank pressure to a predetermined low sensed pressure which will turn on the pump to refill the tank.
Most accumulator tanks provide a flexible barrier between the air and water to prevent the loss of air and, therefore, air pressure in the system. The technique in which air and water is separated may be by employing a diaphragm or flexible membrane which is attached to the inner wall of the tank to separate the air from the water. A second technique is to employ an air cell wherein a sealed bladder containing air is positioned in the tank with access to the interior of the bladder by an exterior air valve. A similar arrangement may be used by containing water within the cell which is surrounded by pressurized air.
While all of these designs have advantages and disadvantages, the most desirable arrangement is a design having a diaphragm attached to the inner side wall of the tank to separate the water and air contained therein. Such a tank operates correctly and in any orientation, and the tank and diaphragm arrangement is more conducive to high production manufacturing techniques. Moreover, a diaphragm-type separator may be constructed from a relatively heavy gauge plastic, or desirably, butyl rubber, and may be shaped to conform to the cross-section of the tank to eliminate stretching.
This arrangement, however, involves the dual problem of providing a pressure tight seal between the mating halves of the pressure vessel and between the side wall of the vessel and the diaphragm. For the sake of economy, attempts have been made to combine the seal between the tank halves and the seal between the diaphragm and the side wall in a single assembly. Such an arrangement is shown in U.S. Pat. No. 4,595,037. The arrangement shown in the patent, however, involves the use of an additional machined ring and an additional O-ring seal in the assembly. The use of additional assembly parts naturally increases the cost of the item. More importantly, however, the assembly shown in U.S. Pat. No. 4,595,037 involves the use of two seals to prevent leakage from the tank liner. Further, traditional tank designs include top and bottom domes as well as a cylindrical side wall. The use of a cylindrical side wall portion does not add to the structural integrity of the pressure vessel and, therefore, wastes material in the manufacture of the vessel.